I have a pair of 250 blowers that I am planning on putting on my 330 mercs. I am not looking for spectacular gains, 3-4 psi and will be running 5-55k rpms. I am looking for input on carb size. I was hoping to run single carbs and when I build new engines add a second carb to the setup. I am not sure if this is possible. Secondly these blowers are off a 575sci which is serpentine, has anyone had experience putting them on an old v-belt engine?

575s had 256 blowers slightly different, and i've heard of poor distribution with single carbs on these, just what ive heard. a pair of 750's will prob be a little more than you need but i think can be made to work.

Not knocking your plans at all, but stock 330's with 4psi and 5500 revs sounds like a recipe for a bilge full of metal fragments. If you are planning to rebuild the engines in teh future anyway, wait until you have the funds / time/ etc. to build them properly. You will be MUCH happier that way.

But to answer your question, you will need about 900 CFM to feed a 454 @ 5500 RPM @ 4psi.

http://www.rbssuperchargers.com/The_...arburation.cfm

According to RBS calculator, I need 1273cfm. However, my twin 850's on top of the Mega Blowers work oh so well. Undersizing the carb on a roots will hurt power. You'll end up having to drive the blower harder to make the boost.

I wouldn't turn more than 5k with the 330 engine. The cast internals are one thing, but the valve springs will likely be the real problem with running boost.

thanks for the replies. you are correct, they are 256s. its just a lake boat so the wot time is minimal. I was wondering about fuel dist. with the single carb but did not want to buy 4 carbs, run them for a season and buy 4 more unless its has to be done.

I know the 330s are not the choice for hp and I am preparing to build more suitable power but this will have to do for now.

any thoughts on the v belt acc. drive working with the 256s. snout length etc???? I just dont want to tear my boat down and find that they will not work. I like to kinda know what I am getting into before i start.

The early 575 had 256 the later ones had 250s

well..........I have one early and one late I think, (im not sure) one has a sight glass and one does not, but they look the same otherwise.

do your self a favor,get in touch with nickerson performance carb. their in pa. set me up with 250's over 11 years ago. running 510's 6.5 lbs on single dominator carb.

A single 1050 will be more than enough carb and you should not have any fuel distribution issues on a 454/330.
Although, putting them on stock 330's is not a great idea to start with.
You don't have enough cam or head flow to spin them past 5k and they are all cast internals.